Project Summary/Abstract Primary sclerosing cholangitis (PSC) is a chronic liver disease that causes cholestasis and inflammation of the bile ducts, which can lead to fibrosis, bile duct cancer, and liver failure. Currently, the only approved treatment for PSC is liver transplantation, yet up to 20% of transplant recipients have recurrence of disease. Therefore, developing therapies to slow disease progression or treating underlying disease processes could offer viable alternatives to transplantation, as there is a clear need for alternative therapies to transplantation. It has been previously shown during injuries to the biliary epithelium and liver subsets of hepatocytes can acquire a cholangiocyte-like. This phenomenon, known as transdifferentiation, may contribute to biliary repair by creating a population of healthy cholangiocyte that could then be expanded to create de novo channels for bile export relieving the effects of toxic bile acids in the liver. However, the mechanisms underlying this transdifferentiation and cholangiocyte expansion are not fully understood. The Wnt/?-catenin pathway is a critical regulator of liver development and physiology and is known to be activated hepatocyte-to-cholangiocyte transdifferentiation under certain conditions. Recently, we discovered that mice expressing a mutated non- degradable form of beta-catenin (S45D) have a significant number of hepatocytes expressing cholangiocyte markers after exposure to 3,5-diethoxycarbonyl-1,4-dihydro-collidine (DDC), a murine model for PSC, compared to wild-type littermates. There was also marked improvement in intrahepatic cholestasis and upregulation of Wnt7A and -7B in the portal triad of the S45D mice fed DDC diet. These observations suggest a novel preclinical opportunity to treat intrahepatic cholestasis by stimulating hepatocyte transdifferentiation and cholangiocyte proliferation through activation of Wnt signaling. Therefore, we hypothesize Wnt signaling prevents cholestasis by promoting hepatocyte transdifferentiation and cholangiocyte proliferation. To test this hypothesis, we propose to study two aims. In aim 1 we will test the hypothesis that Wnt7A drives hepatocyte transdifferentiation by lineage tracing Wnt7A/beta-catenin driven hepatocyte transdifferentiation in two in vitro models, cell culture and organoid culture, and one in vivo model, S45D mice on DDC diet. In aim 2 we will test the hypothesis that Wnt7B induces cholangiocyte proliferation by using cholangiocyte specific Wnt7B KO mice and placing the mice on DDC diet. Completion of our proposed experiments will define the roles of Wnt7A and, -7B in bile duct regeneration. These finding could become the foundation of a novel treatment for PSC, which utilizes Wnt to promote bile duct regeneration, producing a new method of treatment for PSC and other similar diseases.